Updated

A small charter boat off New Zealand capsized Saturday morning in what may have been a collision with a whale, leaving five people dead.

The incident occurred near the South Island town of Kaikōura.

Six others on the boat were rescued, although authorities are continuing to investigate the cause of the accident.

Kaikōura Police Sergeant Matt Boyce said all of the survivors were assessed to be in stable condition at a local health center, with one transferred to a hospital in the city of Christchurch as a precaution.

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Police divers had recovered the bodies of the deceased, but they were still notifying the relatives of the victims and could not yet publicly name them.

In a statement, they said that a boat ramp had been blocked off from the public. 

"Our thoughts are with everyone involved, including the victims and their families, their local communities, and emergency services personnel," he said.

Kaikōura Mayor Craig Mackle told The Associated Press that the water was calm at the time of the accident, so the assumption was that a whale had surfaced from beneath the boat. 

The official said locals had helped with rescue efforts after the collision, but that the water was very cold and they feared for the outcome of anyone who had fallen overboard.

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Sperm whales and humpback whales have been in the region and Kaikōura is a popular whale-watching destination. 

"It always plays on your mind that it could happen," he said, adding that he hadn’t heard about any previous such accidents.

Mackle said the boat was a charter vessel typically used for fishing excursions and New Zealand news outlet Stuff reported that the passengers belonged to a bird enthusiasts' group.

One local, Vanessa Chapman, who watched the rescue efforts from Goose Bay, which is located near Kaikōura, told Stuff she saw a person sitting on top of an overturned boat after the collision waving their arms.

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Chapman said two rescue helicopters and a local helicopter were circling before a couple of divers jumped out. She said the person atop the boat was rescued and that it appeared a second person was pulled from the water.

Compliance agency Maritime New Zealand said it had sent two investigators to the scene and would be conducting a thorough investigation once recovery operations had concluded.

The Associated Press contributed to this report.